Abstract
In this study, a PdAl (20 nm)/Au (30 nm) metal stack scheme is used for forming low-ohmic-resistance contact on Mg-doped (1.5 × 1017 cm−3) p-type AlGaN at various annealing temperatures. Using a circular-transmission line model, the specific contact resistance (ρc) of PdAl/Au/p-AlGaN ohmic contact is determined via the current–voltage (I–V) characteristics. As-deposited contacts demonstrate non-linear behavior. However, the contact exhibits linear I–V characteristics with excellent ohmic contact of ρc = 1.74 × 10−4Ωcm2, when annealed at 600 °C for 1 min in a N2 atmosphere. The Ga and Al vacancies created at the PdAl/Au and p-AlGaN interfaces, which act as acceptors to increase the hole concentration at the interface. The out-diffusion of Ga as well as in-diffusion of Pd and Au to form interfacial chemical reactions at the interface is observed by X-ray photoelectron spectroscopy (XPS) measurements. The phases of the Ga–Pd and Ga–Au phases are detected by X-ray diffraction (XRD) analysis. Morphological results show that the surface of the contact is reasonably smooth with the root-mean-square roughness of 2.89 nm despite annealing at 600 °C. Based on the above experimental considerations, PdAl/Au/p-AlGaN contact annealed at 600 °C is a suitable p-ohmic contact for the development of high-performance electronic devices.
Highlights
The development of high-performance ohmic metal contacts on n/p-type AlGaN and n/p-typeInGaN is increasing their potential for use in high-quality electro-optic devices, such as laser diodes, light-emitting diodes, and high-power/frequency high-electron-mobility transistors (HEMTs) [1,2,3,4].Various metallization schemes, such as the use of Ti/Al, Ti/Ta/Al, Ta/Ti/Al, and Ti/Al/(Ti, Ni, Mo, Pd, and Pt)/Au, were used as ohmic contacts for n-type AlGaN [5,6,7,8]
A non-linear I–V behavior was observed in the as-deposited PdAl/Au/p-AlGaN ohmic contact, but the curve became linear when the contact was annealed at 400 ◦ C and the slope of the curve increased as the annealing temperature increased up to 600 ◦ C
We experimentally studied the PdAl/Au metal stack on Mg-doped p-AlGaN for fabricating high-performance, highly reliable ohmic contacts
Summary
InGaN is increasing their potential for use in high-quality electro-optic devices, such as laser diodes, light-emitting diodes, and high-power/frequency high-electron-mobility transistors (HEMTs) [1,2,3,4]. Various metallization schemes, such as the use of Ti/Al, Ti/Ta/Al, Ta/Ti/Al, and Ti/Al/(Ti, Ni, Mo, Pd, and Pt)/Au, were used as ohmic contacts for n-type AlGaN [5,6,7,8]. Blank et al [9] found a potential barrier of approximately
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